Certain aryl substituted imidazopyrazinones: a new class of GABA brain receptor ligands

ABSTRACT

This invention encompasses compounds of formula I: ##STR1## or the pharmaceutically acceptable non-toxic salts thereof wherein: ##STR2## represents: ##STR3##  where n is 0, 1, or 2; R 1  and R 2  are hydrogen or straight or branched chain alkyl groups; 
     Y represents various organic and inorganic substituents; 
     W represents an aromatic group substituted with various organic and inorganic substituents; 
     A is CH or N; 
     B is a substituted or unsubstituted carbon or N; and 
     E is hydrogen or straight or branched alkyl groups. 
     These compounds are highly selective agonists, antagonists or inverse agonists for GABAa brain receptors or prodrugs thereof and are useful in the diagnosis and treatment of anxiety, sleep, and seizure disorders, overdose with benzodiazepine type drugs, and enhancement of alertness.

This is a continuation of application Ser. No. 08/495,521, filed Dec. 21, 1995, now U.S. Pat. No. 6,610,299, which is a National Phase application of PCT/US94/00109, filed Jan. 4, 1994, which is a continuation of application Ser. No. 08/001,258 filed Jan. 6, 1993 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to certain aryl substituted imidazopyrazinones which selectively bind to GABAa receptors. This invention also relates to pharmaceutical compositions comprising such compounds. It further relates to the use of such compounds in treating anxiety, sleep and seizure disorders, and overdoses of benzodiazepine-type drugs, and enhancing alertness. The interaction of imidazopyazinones of the invention with a GABA binding site, the benzodiazepines (BDZ) receptor, is described. This interaction results in the pharmacological activities of these compounds.

2. Description of the Related Art

γ-Aminobutyric acid (GABA) is regarded as one of the major inhibitory amino acid transmitters in the mammalian brain. Over 30 years have elapsed since its presence in the brain was demonstrated (Roberts & Frankel, J. Biol. Chem 187: 55-63, 1950: Udenfriend, J. Biol. Chem. 187: 65-69, 1950). Since that time, an enormous amount of effort has been devoted to implicating GABA in the etiology of seizure disorders, sleep, anxiety and cognition (Tallman and Gallager, Ann. Rev. Neuroscience 8: 21-44, 1985). Widely, although unequally, distributed through the mammalian brain, GABA is said to be a transmitter at approximately 30% of the synapses in the brain. In most regions of the brain, GABA is associated with local inhibitory neurons and only in two regions is GABA associated with longer projections. GABA mediates many of its actions through a complex of proteins localized both on cell bodies and nerve endings; these are called GABAa receptors. Postsynaptic responses to GABA are mediated through alterations in chloride conductance that generally, although not invariably, lead to hyperpolarization of the cell. Recent investigations have indicated that the complex of proteins associated with postsynaptic GABA responses is a major site of action for a number of structurally unrelated compounds capable of modifying postsynaptic responses to GABA. Depending on the mode of interaction, these compounds are capable of producing a spectrum of activities (either sedative, anxiolytic, and anticonvulsant, or wakefulness, seizures, and anxiety).

1,4-Benzodiazepines continue to be among the most widely used drugs in the world. Principal among the benzodiiazepines marketed are chlordiazepoxide, diazepam, flurazepam, and triazolam. These compounds are widely used as anxiolytics, sedative-hypnotics, muscle relaxants, and anticonvulsants. A number of these compounds are extremely potent drugs; such potency indicates a site of action with a high affinity and specificity for individual receptors. Early electrophysiological studies indicated that a major action of benzodiazepines was enhancement of GABAergic inhibition. The benzodiazepines were capable of enhancing presynaptic inhibition of a monosynaptic ventral root reflex, a GABA-mediated event (Schmidt et al., 1967, Arch. Exp. Path. Pharmakol. 258: 69-82). All subsequent electrophysiological studies (reviewed in Tallman et al. 1980. Science 207:274-81, Haefley et al., 1981, Handb. Exptl. Pharmacol. 33:95-102) have generally confirmed this finding, and by the mid-1970s, there was a general consensus among electrophysiologists that the benzodiazepines could enhance the actions of GABA.

With the discovery of the "receptor" for the benzodiazepines and the subsequent definition of the nature of the interaction between GABA and the benzodiazepines, it appears that the behaviorally important interactions of the benzodiazepines with different neurotransmitter systems are due in a large part to the enhanced ability of GABA itself to modify these systems. Each modified system, in turn, may be associated with the expression of a behavior.

Studies on the mechanistic nature of these interactions depended on the demonstration of a high-affinity benzodiazepine binding site (receptor). Such a receptor is present in the CNS of all vertebrates phylogenetically newer than the boney fishes (Squires & Braestrup 1977, Nature 166: 732-34, Mohler & Okada, 1977, Science 198: 854-51, Mohler & Okada. 1977. Br. J. Psychiatry 133: 261-68). By using tritiated diazepam, and a variety of other compounds, it has been demonstrated that these benzodiazepine binding sites fulfill many of the criteria of pharmacological receptors; binding to these sites in vitro is rapid, reversible, stereospecific, and saturable. More importantly, highly significant correlations have been shown between the ability of benzodiazepines to displace diazepam from its binding site and activity in a number of animal behavioral tests predictive of benzodiazepine potency (Braestrup & Squires 1978. Br. J. Psychiatry 133: 249-60, Mohler & Okada, 1977, Science 198: 854-51, Mohler & Okada. 1977, Br. J. Psychiatry 133: 261-68). The average therapeutic doses of these drugs in man also correlate with receptor potency (Tallman et al. 1980. Science 207: 274-281).

In 1978, it became clear that GABA and related analogs could interact at the low affinity (1 μM) GABA binding site to enhance the binding of benzodiazepines to the clonazepan-sensitive site (Tallman et al. 1978, Nature, 274: 383-85). This enhancement was caused by an increase in the affinity of the benzodiazepine binding site due to occupancy of the GABA site. The data were interpreted to mean that both GABA and benzodiazepine sites were allosterically linked in the membrane as part of a complex of proteins. For a number of GABA analogs, the ability to enhance diazepam binding by 50% of maximum and the ability to inhibit the binding of GABA to brain membranes by 50% could be directly correlated. Enhancement of benzodiazepine binding by GABA agonists is blocked by the GABA receptor antagonist (+) bicuculline; the stereoisomer (-) bicuculline is much less active (Tallman et al., 1978, Nature, 274: 383-85).

Soon after the discovery of high affinity binding sites for the benzodiazepines, it was discovered that a triazolopyridazine could interact with benzodiazepine receptors in a number of regions of the brain in a manner consistent with receptor heterogeneity or negative cooperativity. In these studies, Hill coefficients significantly less than one were observed in a number of brain regions, including cortex, hippocampus, and striatum. In cerebellum, triazolopyridazine interacted with benzodiazepine sites with a Hill coefficient of 1 (Squires et al., 1979. Pharma. Biochem. Behav. 10: 825-30, Klepner et al. 1979, Pharmacol. Biochem. Behav. 11: 457-62). Thus, multiple benzodiazepine receptors were predicted in the cortex, hippocampus, striatum, but not in the cerebellum.

Based on these studies, extensive receptor autoradiographic localization studies were carried out at a light microscopic level. Although receptor heterogeneity has been demonstrated (Young & Kuhar 1980, J. Pharmacol. Exp. Ther. 212: 337-46, Young et al., 1981 J. Pharmacol Exp. ther 216: 425-430. Niehoff et al. 1982, J. Pharmacol. Exp. Ther. 221: 670-75), no simple correlation between localization of receptor subtypes and the behaviors associated with the region has emerged from the early studies. In addition, in the cerebellum, where one receptor was predicted from binding studies, autoradiography revealed heterogeneity of receptors (Niehoff et al., 1982, J. Pharmacol, Exp. Ther. 221: 670-75).

A physical basis for the differences in drug specificity for the two apparent subtypes of benzodiazepine sites has been demonstrated by Sieghart & Karobath. 1980, Nature 286: 285-87. Using gel electrophoresis in the presence of sodium dodecyl sulfate, the presence of several molecular weight receptors for the benzodiazepines has been reported. The receptors were identified by the covalent incorporation of radioactive flunitrazepam, a benzodiazepine which can covalently label all receptor types. The major labeled bands have moelcular weights of 50,000 to 53,000, 55,000. and 57,000 and the triazolopyridazines inhibit labeling of the slightly higher molecular weight forms (53,000, 55,000, 57,000) (Seighart et al. 1983, Eur. J. Pharmacol. 88: 291-99).

At that time, the possibility was raised that the multiple forms of the receptor represent "isoreceptors" or multiple allelic forms of the receptor (Tallman & Gallager 1985. Ann. Rev. Neurosci. 8, 21-44). Although common for enzymes, genetically distinct forms of receptors have not generally been described. As we begin to study receptors using specific radioactive probes and electrophoretic techniques, it is almost certain that isoreceptors will emerge as important in investigations of the etiology of psychiatric disorders in people.

The GABAa receptor subunits have been cloned from bovine and human cDNA libraries (Schoenfield et al., 1988, Duman et al., 1989). A number of distinct cDNAs were identified as subunits of the GABAa receptor complex by cloning and expression. These are categorized into ∝, β, γ, δ, ε, and provide a molecular basis for the GABAa receptor heterogeneity and distinctive regional pharmacology (Shivvers et al., 1980; Levitan et al., 1989). The γ subunit appears to enable drugs like benzodiazepines to modify the GABA responses (Pritchett et al., 1989). The presence of low Hill coefficients in the binding of ligands to the GABAa receptor indicates unique profiles of subtype specific pharmacological action.

Drugs that interact at the GABAa receptor can possess a spectrum of pharmacological activities depending on their abilities to modify the actions of GABA. For example, the beta-carbolines were first isolated based upon their ability to inhibit competitively the binding of diazepam to its binding site (Nielsen et al., 1979. Life Sci. 25: 679-86). The receptor binding assay is not totally predictive about the biological activity of such compounds: agonists, partial agonists, inverse agonists, and antagonists can inhibit binding. When the beta-carboline structure was determined, it was possible to synthesize a number of analogs and test these compounds behaviorally. It was immediately realized that the beta-carbolines could antagonize the actions of diazepam behaviorally (Tenen & Hirsch, 1980, Nature 288: 609-10). In addition to this antagonism, beta-carbolines possess intrinsic activity of their own opposite to that of the benzodiazepines; they become known as inverse agonists.

In addition, a number of other specific antagonists of the benzodiazepine receptor were developed based on their ability to inhibit the binding of benzodiazepines. The best studied of these compounds is an imidazodiazepine. (Hunkeler et al., 1981, Nature 290: 514-516). This compound is a high affinity competitive inhibitor of benzodiazepine and beta-carboline binding and is capable of blocking the pharmacological actions of both these classes of compounds. By itself, it possesses little intrinsic pharmacological activity in animals and humans (Hunkeler et al., 1981, Nature 290: 514-16; Darragh et al., 1983. Eur. J. Clin. Pharmacol. 14: 569-70). When a radiolabeled form of this compound was studied (Mohler & Richards, 1981, Nature 294: 763-65), it was demonstrated that this compound would interact with the same number of sites as the benzodiazepines and beta-carbolines, and that the interactions of these compounds were purely competitive. This compound is the ligand of choice for binding to GABAa receptors because it does not possess receptor subtype specificity and measures each state of the receptor.

The study of the interactions of a wide variety of compounds similar to the above has led to the categorizing of these compounds. Presently, those compounds possessing activity similar to the benzodiazepines are called agonists. Compounds possessing activity opposite to benzodiazepines are called inverse agonists, and the compounds blocking both types of activity have been termed antagonists. This categorization has been developed to emphasize the fact that a wide variety of compounds can produce a spectrum of pharmacological effects, to indicate that compounds can interact at the same receptor to produce opposite effects, and to indicate that beta-carbolines and antagonists with intrinsic anxiogenic effects are not synonymous.

A biochemical test for the pharmacological and behavioral properties of compounds that interact with the benzodiazepine receptor continues to emphasize the interaction with the GABAergic system. In contrast to the benzodiazepines, which show an increase in their affinity due to GABA (Tallman et al., 1978. Nature 274: 383-85. Tallman et al., 1980, Science 207: 274-81), compounds with antagonist properties show little GABA shift (i.e., change in receptor affinity due to GABA) (Mohler & Richards 1981, Nature 294: 763-65), and the inverse agonists actually show a decrease in affinity due to GABA (Braestrup & Nielson 1981, Nature 294: 472-474). Thus, the GABA shift predicts generally the expected behavioral properties of the compounds.

Various compounds have been prepared as benzodiazepine agonists and antagonists. "For Example, U.S. Pat. Nos. 3,455,943, 4,435,403, 4,596,808, 4,623,649, and 4,719,210, German Patent No. DE 3,246,932, and Liebigs Ann. Chem. 1986, 1749 teach assorted benzodiazepine agonists and antagonists and related anti-depressant and central nervous system active compounds. U.S. Pat. No. 3,455,943 disclosed compounds of the formula: ##STR4## wherein R₁ is a member of the group consisting of hydrogen and lower alkoxy; R₂ is a member of the group consisting of hydrogen and lower alkoxy; R₃ is a member of the group consisting of hydrogen and lower alkyl; and X is a divalent radical selected from the group consisting of ##STR5## and the non-toxic acid addition salts thereof.

U.S. Pat. No. 4,435,403 teaches compounds of the formula: ##STR6## wherein

R^(C) is hydrogen, lower alkyl, alkoxyalkyl of up to 6 C-atoms, cycloalkyl of 3-6 C-atoms, aralkyl of up to 8 C-atoms, or (CH₂)_(n) OR²⁰

wherein R²⁰ is alkyl of up to 6 C-atoms, cycloalkyl of 3-6 C-atoms or aralkyl of up to 8 C-atoms and n is an integer of 1 to 3;

Y is oxygen, two hydrogen atoms or NOR¹,

wherein R¹ is hydrogen, lower alkyl, aryl or aralkyl of up to 6 C-atoms, COR², wherein R² is lower alkyl of up to 6 C-atoms,

or Y is CHCOOR³, wherein R³ is hydrogen or lower alkyl

or Y is NNR⁴ R⁵,

wherein R⁴ and R⁵ can be the same or different and each is hydrogen, lower alkyl, C₆₋₁₀ -aryl, C₇₋₁₀ -aralkyl or CONR⁶ R⁷,

wherein R⁶ and R⁷ can be the same or different and each is hydrogen or lower alkyl or R⁴ and R⁵ together with the connecting N-atom, form a 5- or 6-membered heterocyclic ring which optionally may also contain an O-atom or up to 3 N-atoms and which optionally may be substituted by a lower alkyl group;

Z is hydrogen, or alkoxy or aralkoxy each of up to 10 C-atoms and each optionally substituted by hydroxy, or Z is alkyl of up to 6 C-atoms. C₆₋₁₀ -aryl or C₇₋₁₀ -aralkyl each of which may optionally be substituted by a COOR⁸ or a CONR⁹ R ¹⁰ group,

wherein R⁸ is alkyl of up to 6 C-atoms, and R⁹ and R¹⁰ can be the same or different and each is hydrogen or alkyl of up to 6 C-atoms; or Z is NR⁹ R¹⁰, wherein R⁹ and R¹⁰ are as defined above; or Z is NR¹¹ CHR¹² R¹³,

wherein R¹¹ and R¹² each is hydrogen or together form a N═C double bond,

wherein R¹³ is C₁₋₁₀ -alkyl or NR¹⁴ R¹⁵,

wherein R¹⁴ and R¹⁵ are the same or different and each is hydrogen, OH or alkyl or alkoxy each of up to 6 C-atoms,

or wherein R¹² and R¹³ together are oxygen, in which case, R¹¹ is hydrogen;

or Z is COOR² wherein R² is as defined above;

or Y and Z, together with the connecting C-atom, may form a 5- or 6-membered heterocyclic ring which contains an O-atom, adjoining O- and N-atoms or up to a 4 N atoms and which optionally may be substituted by a lower alkyl group, hydroxy or oxo.

U.S. Pat. No. 4,596,808 discloses compounds of the formula: ##STR7## wherein

R^(A) is H, F, CL, Br, I, NO₂, CN, CH₃, CF₃, SCH₃, NR¹⁶ R¹⁷ or NHCOR¹⁶,

wherein R¹⁶ of R¹⁷ are the same or different and each is hydrogen or alkyl, alkenyl or alkynyl each of up to 6 C-atoms, aralkyl or cycloalkyl each of up to 10 C-atoms,

or wherein R¹⁶ and R¹⁷ together form a saturated or unsaturated 3-7 membered heterocyclic ring.

U.S. Pat. No. 4,623,649 teaches compounds of the formula: ##STR8## wherein

R³ is an oxadiazolyl residue of the formula ##STR9## wherein R⁵ stands for lower alkyl of up to 3 carbon atoms or an ester --CO₂ R₆

with R⁶ being hydrogen or lower alkyl of up to 3 carbon atoms,

R⁴ is hydrogen, lower alkyl of up to 3 carbon atoms, or CH₂ OR⁹ wherein

R⁹ is lower alkyl of up to 3 carbon atoms,

R^(A) is phenyl or a hydrocarbon residue containing 2-10 carbon atoms which can be cyclic or acyclic, saturated or unsaturated, branched or unbranched, and which can optionally be substituted by oxo. formyl OH, O-alkyl of up to 3 carbon atoms or phenyl, and wherein in a cyclic hydrocarbon residue, a CH₂ -group can be replaced by oxygen.

U.S. Pat. No. 4,719,210 discloses compounds of the formula: ##STR10## wherein

R¹ is hydrogen or a protecting group,

R² is --CH═CR⁴ ₂ or --C═CR⁴,

R⁴ is hydrogen or halogen,

R³ is hydrogen, lower alkyl or lower alkoxyalkyl,

R^(A) is, inter alia, hydrogen, OR⁷, lower alkyl, which optionally is substituted with aryl, lower alkoxy or NR5R6,

R⁵ and R⁶ can be the same or different and in each case is hydrogen, lower alkyl or together with the nitrogen atom a 5-6 member ring, which can contain another heteroatom.

R⁷ is lower alkyl, optionally substituted aryl or aralkyl, and each compound can contain one or more R^(A) radicals which are not hydrogen.

These compounds differ from the compounds of the present invention. These U.S. patents teach carbocyclic compounds having pyridine or piperidine rings but lacking the pyrimidine ring present in the compounds of the present invention.

German Patent No. DE 3,246,932 discloses compounds of the formula: ##STR11## wherein

R=halo. NO₂, CO₂ H, modified CO₂ H, R² O, R² S(O)_(n) ; n=0-2; and R¹ =H, alkyl, cycloalkyl, aralkyl, aryl, CO₂ H, amino R² O, R² S(O)_(n).

Liebigs Ann. Chem. 1986, 1749-1764 teaches compounds of the formula: ##STR12##

Where R^(X) is hydrogen, methyl, benzyloxy, or methoxy, and R³ is carboethoxy.

These compounds differ from the compounds of the present invention. These compounds are not imidazopyazinones and also lack the various ring substituents of the compounds of the present invention.

SUMMARY OF THE INVENTION

This invention provides novel compounds of Formula I which interact with a GABAa binding site, the benzodiazepine receptor.

The invention provides pharmaceutical compositions comprising compounds of Formula I. The compounds of Formula I are useful in enhancing alertness, treatment of seizure, anxiety, and sleep disorders, and treatment of benzodiazepine overdoses. Accordingly, a broad embodiment of the invention is directed to compounds of general Formula I: ##STR13## or the pharmaceutically acceptable non-toxic salts thereof wherein: ##STR14## represents ##STR15## and n is 0, 1 or 2;

R₁ and R₂ are the same or different and represent hydrogen or straight or branched chain lower alkyl having 1-6 carbon atoms;

W is phenyl, 2- or 3-thienyl, or 2-, 3-, or 4-pyridyl; or phenyl, 2- or 3-thienyl, or 2-, 3-, or 4-pyridyl, each of which is mono or disubstituted with halogen, hydroxy, straight or branched chain lower alkyl having 1-6 carbon atoms, straight or branched chain lower alkoxy having 1-6 carbon atoms, amino or mono- or dialkylamino where each alkyl portion is straight or branched chain lower alkyl having 1-6 carbon atoms;

Y is N--R₃ where R₃ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms; straight or branched chain lower alkoxy having 1-6 carbon atoms, or phenylalkoxy where the alkoxy is straight or branched chain lower alkoxy having 1-6 carbon atoms; or

--COR₄ or --SO₂ R₄ where R₄ is straight or branched chain lower alkyl having 1-6 carbon atoms;

C═O, CR₆ OR₅, CR₆ COR₅, CR₆ CO₂ R₅, CR₆ OCOR₅, and CR₅ R₆, where R₅ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms; and R₆ is hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms;

CR₆ CONR₇ R₈ or CR₆ (CH₂)_(q) NR₇ R₈ where q is 0, 1, or 2, and R₆ and R₇ are the same or different and represent hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms; and R₈ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, pyridyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms; or NR₇ R₈ is morpholyl, piperidyl, pyrrolidyl, or N-alkyl piperazyl;

CR₆ NR₉ CO₂ R₁₀ where R₆ is hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms, and R₉ and R₁₀ are the same or different and represent hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms;

CR₆ C(OH)R₁₁ R₁₂ where R₁₁ and R₁₂ are the same or different and represent straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms, and R₆ is hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms: or

Y is a group of the formula: ##STR16## where m is 0, 1, or 2.

R₁₃ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms;

Z is methylene, oxygen, NR₁₄ or CHCONR₁₄ where R₁₄ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, pyridyl, or phenylalkyl or pyridylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms; and

T is methylene or oxygen;

A is CH or N;

B is N or CR₁₅ where

R₁₅ is hydrogen, halogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms,

--CONR₁₆ R₁₇, --COR₁₆ or --SO₂ R₁₈ where R₁₆ is straight or branched chain lower alkyl having 1-6 carbon atoms, straight or branched chain lower alkoxy having 1-6 carbon atoms, phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms, or phenylalkoxy where the alkoxy is straight or branched chain alkoxy having 1-carbon atoms and R₁₇ is straight or branched chain lower alkyl having 1-6 carbon atoms; R₁₈ is straight or branched chain lower alkyl having 1-6 carbon atoms, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms; and

E is hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms.

These compounds are highly selective agonists, antagonists or inverse agonists for GABAa brain receptors or prodrugs thereof. In other words, while the compounds of the invention all interact with GABAa brain receptors, they do not display identical physiologic activity. Thus these compounds are useful in the diagnosis and treatment of anxiety, sleep, and seizure disorders, overdose with benzodiazepline drugs, and enhancement of memory. For example, these compounds can easily be used to treat overdoses of benzodiazopine-type drugs as they would competitively bind to the benzodiazepine receptor.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1-4 show representative imidazopyazinones of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The novel compounds encompassed by the instant invention can be described by general formula I.

The present invention also encompasses compounds of general formula II: ##STR17##

or the pharmaceutically acceptable non-toxic salts thereof wherein: n, R₁, R₂, R₅, and W are as defined above.

The present invention also encompasses compounds of general formula III: ##STR18##

or the pharmaceutically acceptable non-toxic salts thereof where R₁, R₂, R₃, and W are as defined above

The present invention also encompasses compounds of general formula IV: ##STR19##

or the pharmaceutically acceptable non-toxic salts thereof where W, Z and Tare as defined above, and U is methylene or carbonyl.

The present invention also encompasses compounds of general formula V: ##STR20##

or the pharmaceutically acceptable non-toxic salts thereof where W, E and R₁₅ are as defined above.

The present invention also encompasses compounds of formula VI: ##STR21##where

R' represents hydrogen or halogen;

R" represents hydrogen or straight or branched chain lower alkoxy having about 1-6 carbon atoms; and

R'" represents hydrogen, halogen or straight or branched chain lower alkoxyhaving about 1-6 carbon atoms.

Preferred compounds of formula VI are those where the halogen is fluorine.

The present invention also encompasses compounds of formula Vlla and Vllb: ##STR22##

or the pharmaceutically acceptable non-toxic salts thereof where R" and R'"independently represent hydrogen, methoxy or ethoxy.

Non-toxic pharmaceutical salts include salts of acids such as hydrochloric,phosphoric, hydrobromic, sulfuric, sulfinic, formic, toluene sulfonic, hydroiodic, acetic and the like. Those skilled in the art will recognize awide variety of non-toxic pharmaceutically acceptable addition salts.

By lower alkyl in the present invention is meant straight or branched chainalkyl groups having 1-6 carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, 2-pentyl, isopentyl, neopentyl, hexyl, 2-hexyl, 3-hexyl, and 3-methylpentyl.

By lower alkoxy in the present invention is meant straight or branched chain alkoxy groups having 1-6 carbon atoms, such as, for example, methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, pentoxy, 2-pentoxy, isopentoxy, neopentoxy, hexoxy, 2-hexoxy, 3-hexoxy, and 3-methylpentoxy.

By halogen in the present invention is meant fluorine, bromine, chlorine, and iodine.

By N-alkyl piperazyl in the invention is meant radicals of the formula: ##STR23##where R is a straight or branched chain lower alkyl as defined above.

Where R₁₅ is --COR₁₆ and R₁₆ is straight or branched chain lower alkoxy or phenylalkoxy, --COR₁₆ represents an alkyl ester or analkyl ester having a phenyl substituent.

Representative compounds of the present invention, which are encompassed byFormula I, include, but are not limited to the compounds in FIGS. 1-4 and their pharmaceutically acceptable salts. The invention also encompasses the tautomeric forms of the compounds of Formula 1.

The pharmaceutical utility of compounds of this invention are indicated by the following assay for GABAa receptor binding activity.

Assays are carried out as described in Thomas and Tallman (J. Bio. Chem. 156: 9838-9842, J. Neurosci. 3:433-440. 1983). Rat cortical tissue is dissected and homogenized in 25 volumes (w/v) of 0.05M Tris HCl buffer (pH7.4 at 4° C.). The tissue homogenate is centrifuged in the cold (4°) at 20,000×g for 20'. The supernatant is decanted and thepellet is rehomogenized in the same volume of buffer and again centrifuged at 20,000×g. The supernatant is decanted and the pellet is frozen at -200° C. overnight. The pellet is then thawed and rehomogenized in 25 volume (original wt/vol) of buffer and the procedure is carried out twice. The pellet is finally resuspended in 50 volumes (w/vol of 0.05M Tris HCl buffer (pH 7.4 at 40° C.).

lncubations contain 100 μl of tissue homogenate. 100 μl of radioligand 0.5 nM (³ H--RO15-1788 ³ H-Flumazenil! specific activity 80 Ci/mmol), drug or blocker and buffer to a total volume of 500 μl. Incubations are carried for 30 min at 4° C. then are rapidlyfiltered through GFB filters to separate free and bound ligand. Filters arewashed twice with fresh 0.05M Tris HCl buffer (pH 7.4 at 4° C.) and counted in a liquid scintillation counter. 1.0 μM diazepam is added to some tubes to determine nonspecific binding. Data are collected in triplicate determinations, averaged and % inhibition of total specific binding is calculated. Total Specific Binding=Total-Nonspecific. In some cases, the amounts of unlabeled drugs is varied and total displacement curves of binding are carried out. Data are converted to a form for the calculation Of IC₅₀ and Hill Coefficient (nH). Data for the compoundsof this invention are listed in Table I.

                  TABLE I                                                          ______________________________________                                         Compound Number.sup.1                                                                           IC.sub.50 (μM)                                             ______________________________________                                         1                0.015                                                         2                0.167                                                         3                0.093                                                         4                0.061                                                         ______________________________________                                          .sup.1 Compound numbers relate to compounds shown in Figures 1-4.        

Compounds 1, 3 and 4 are particularly preferred embodiments of the present invention because of their potency in binding to the GABAa receptor.

The compounds of general formula I may be administered orally, topically, parenterally, by inhalation or spray or rectally in dosage unit formulations containing conventional non-toxic pharmaceutically acceptablecarriers, adjuvants and vehicles. The term parenteral as used herein includes subcutaneous injections, intravenous, intramuscular, intrasternalinjection or infusion techniques. In addition, there is provided a pharmaceutical formulation comprising a compound of general formula I and a pharmaceutically acceptable carrier. One or more compounds of general formula I may be present in association with one or more non-toxic pharmaceutically acceptable carriers and/or diluents and/or adjuvants and if desired other active ingredients. The pharmaceutical compositions containing compounds of general formula I may be in a form suitable for oral use, for example, as tablets, troches, lozenges, aqueous or oily suspensions, dispersible powders or granules, emulsion, hard or soft capsules, or syrups or elixirs.

Compositions intended for oral use may be prepared according to any method known to the art for the manufacture of pharmaceutical compositions and such compositions may contain one or more agents selected from the group consisting of sweetening agents, flavoring agents, coloring agents and preserving agents in order to provide pharmaceutically elegant and palatable preparations. Tablets contain the active ingredient in admixturewith non-toxic pharmaceutically acceptable excipients which are suitable for the manufacture of tablets. These excipients may be for example, inertdiluents, such as calcium carbonate, sodium carbonate, lactose, calcium phosphate or sodium phosphate; granulating and disintegrating agents, for example, corn starch, or alginic acid; binding agents, for example starch,gelatin or acacia, and lubricating agents, for example magnesium stearate, stearic acid or talc. The tablets may be uncoated or they may be coated byknown techniques to delay disintegration and absorption in the gastrointestinal tract and thereby provide a sustained action over a longer period. For example, a time delay material such as glyceryl monosterate or glyceryl distearate may be employed.

Formulations for oral use may also be presented as hard gelatin capsules wherein the active ingredient is mixed with an inert solid diluent, for example, calcium carbonate, calcium phosphate or kaolin, or as soft gelatin capsules wherein the active ingredient is mixed with water or an oil medium, for example peanut oil, liquid paraffin or olive oil.

Aqueous suspensions contain the active materials in admixture with excipients suitable for the manufacture of aqueous suspensions. Such excipients are suspending agents, for example sodium carboxymethylcellulose, methylcellulose, hydropropylmethylcellulose, sodium alginate, polyvinylpyrrolidone, gum tragacanth and gum acacia; dispersing or wetting agents may be a naturally-occurring phosphatide, forexample, lecithin, or condensation products of an alkylene oxide with fattyacids, for example polyoxyethylene stearate, or condensation products of ethylene oxide with long chain aliphatic alcohols, for example heptadecaethyleneoxycetanol, or condensation products of ethylene oxide with partial esters derived from fatty acids and a hexitol such as polyoxyethylene sorbitol monooleate, or condensation products of ethylene oxide with partial esters derived from fatty acids and hexitol anhydrides,for example polyethylene sorbitan monooleate. The aqueous suspensions may also contain one or more preservatives, for example ethyl, or n-propyl p-hydroxybenzoate, one or more coloring agents, one or more flavoring agents, and one or more sweetening agents, such as sucrose or saccharin.

Oily suspensions may be formulated by suspending the active ingredients in a vegetable oil, for example arachis oil, olive oil, sesame oil or coconutoil, or in a mineral oil such as liquid paraffin. The oily suspensions may contain a thickening agent, for example beeswax, hard paraffin or cetyl alcohol. Sweetening agents such as those set forth above, and flavoring agents may be added to provide palatable oral preparations. These compositions may be preserved by the addition of an anti-oxidant such as ascorbic acid.

Dispersible powders and granules suitable for preparation of an aqueous suspension by the addition of water provide the active ingredient in admixture with a dispersing or wetting agent, suspending agent and one or more preservatives. Suitable dispersing or wetting agents and suspending agents are exemplified by those already mentioned above. Additional excipients, for example sweetening, flavoring and coloring agents, may also be present.

Pharmaceutical compositions of the invention may also be in the form of oil-in-water emulsions. The oily phase may be a vegetable oil, for exampleolive oil or arachis oil, or a mineral oil, for example liquid paraffin or mixtures of these. Suitable emulsifying agents may be naturally-occurring gums, for example gum acacia or gum tragacanth, naturally-occurring phosphatides, for example soy bean, lecithin, and esters or partial estersderived from fatty acids and hexitol, anhydrides, for example sorbitan monoleate, and condensation products of the said partial esters with ethylene oxide, for example polyoxyethylene sorbitan monoleate. The emulsions may also contain sweetening and flavoring agents.

Syrups and elixirs may be formulated with sweetening agents, for example glycerol, propylene glycol, sorbitol or sucrose. Such formulations may also contain a demulcent, a preservative and flavoring and coloring agents. The pharmaceutical compositions may be in the form of a sterile injectable aqueous or oleaginous suspension. This suspension may be formulated according to the known art using those suitable dispersing or wetting agents and suspending agents which have been mentioned above. The sterile injectable preparation may also be sterile injectable solution or suspension in a non-toxic parenterally acceptable diluent or solvent, for example as a solution in 1.3-butanediol. Among the acceptable vehicles andsolvents that may be employed are water, Ringer's solution and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solvent or suspending medium. For this purpose any bland fixed oil may be employed including synthetic mono-or diglycerides. In addition, fatty acids such as oleic acid find use in the preparation of injectables.

The compounds of general formula I may also be administered in the form of suppositories for rectal administration of the drug. These compositions can be prepared by mixing the drug with a suitable non-irritating excipient which is solid at ordinary temperatures but liquid at the rectaltemperature and will therefore melt in the rectum to release the drug. Suchmaterials are cocoa butter and polyethylene glycols.

Compounds of general formula I may be administered parenterally in a sterile medium. The drug, depending on the vehicle and concentration used,can either be suspended or dissolved in the vehicle. Advantageously, adjuvants such as local anaesthetics, preservatives and buffering agents can be dissolved in the vehicle.

Dosage levels of the order of from about 0.1 mg to about 140 mg per kilogram of body weight per day are useful in the treatment of the above-indicated conditions (about 0.5 mg to about 7 g per patient per day). The amount of active ingredient that may be combined with the carrier materials to produce a single dosage form will vary depending uponthe host treated and the particular mode of administration. Dosage unit forms will generally contain between from about 1 mg to about 500 mg of anactive ingredient.

It will be understood, however, that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, route of administration, and rate of excretion, drug combination and the severity of the particular disease undergoing therapy.

An illustration of the preparation of compounds of the present invention isgiven in Scheme I. Those having skill in the art will recognize that the starting materials may be varied and additional steps employed to produce compounds encompassed by the present invention, as demonstrated by the following examples. ##STR24##wherein: ##STR25##represents: ##STR26##and n is 0, 1 or 2;

R₁ and R₂ are the same or different and represent hydrogen or straight or branched chain lower alkyl having 1-6 carbon atoms;

W is phenyl, 2- or 3-thienyl, or 2-, 3-, or 4-pyridyl; or phenyl. 2- or 3-thienyl, or 2-, 3-, or 4-pyridyl, each of which is mono or disubstitutedwith halogen, hydroxy, straight or branched chain lower alkyl having 1-6 carbon atoms, straight or branched chain lower alkoxy having 1-6 carbon atoms, amino, or mono- or dialkyl amino where each alkyl portion is straight or branched chain lower alkyl having 1-6 carbon atoms;

Y is N--R₃ where R₃ is hydrogen, straight or branched chain loweralkyl having 1-6 carbon atoms, phenyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms:, straight or branched chain lower alkoxy having 1-6 carbon atoms, or phenylalkoxy where the alkoxy is straight or branched chain lower alkoxy having 1-6 carbon atoms; or

--COR₄ or --SO₂ R₄ where R₄ is straight or branched chain lower alkyl having 1-6 carbon atoms;

C═O, CR₆ OR₅, CR₆ COR₅, CR₆ CO₂ R₅, CR₆ OCOR₅, and CR₅ R₆, where R₅ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, orphenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms; and R₆ is hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms:

CR₆ CONR₇ R₈ or CR₆ (CH₂)_(q) NR₇ R₈ where q is 0, 1, or 2, and R₆ and R₇ are the same or different and represent hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms; and R₈ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, pyridyl, or phenylalkyl wherethe alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms; or NR₇ R₈ is morpholyl, piperidyl, pyrrolidyl, or N-alkylpiperazyl;

CR₆ NR₉ CO₂ R₁₀ where R₆ is hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms, and R_(R) and R₁₀ are the same or different and represent hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, or phenylalkylwhere the alkyl is straight or branched chain lower alkyl having 1-6 carbonatoms:

CR₆ C(OH)R₁₁ R₁₂ where R₁₁ and R₁₂ are the same ordifferent and represent straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms, and R₆ is hydrogen, or straight or branched chain lower alkyl having, 1-6 carbon atoms; or

Y is a group of the formula: ##STR27##where m is 0, 1 or 2.

R₁₃ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, or phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms;

Z is methylene, oxygen, NR₁₄ or CHCONR₁₄ where R₁₄ is hydrogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, pyridyl, or phenylalkyl or pyridylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms; and

T is methylene or oxygen.

A is CH or N;

B is N or CR₁₅ where R₁₅ is hydrogen, halogen, straight or branched chain lower alkyl having 1-6 carbon atoms, phenyl, phenylalkyl where the alkyl is straight or branched chain lower alkyl having 1-6 carbon atoms,

--COOR₁₆, --CONR₁₆ R₁₇, --COR₁₆ or --SO₂ R₁₆ where R₁₆ is straight or branched chain lower alkyl having 1-6 carbonatoms, straight or branched chain lower alkoxy having 1-6 carbon atoms, or phenylalkyl where the alkyl is straight or branched chain lower alkoxy having 1-6 carbon atoms, and R₁₇ is straight or branched chain lower alkyl having 1-6 carbon atoms; and

E is hydrogen, or straight or branched chain lower alkyl having 1-6 carbon atoms.

The invention is illustrated further by the following examples which are not to be construed as limiting the invention in scope or spirit to the specific procedures and compounds described in them.

EXAMPLE I ##STR28##

A mixture of 2-Hydroxymethyl-benzimidazole (11.9 g) and MnO₂ (59.5 g in ethanol (250 mL) was vigorously stirred for 2 days. The reaction was concentrated in vacuo, hot dimethylformamide was added and the mixture wasfiltered through celite. After removal of the solvent in vacuo the tan solid was triturated with ethanol to afford 2-Benzimidazolecarboxaldehyde as a tan powder.

EXAMPLE II ##STR29##

A mixture of 2-benzimidazolecarboxaldehyde (154 mg), 4-Methoxyphenylglycineethyl ester (220 mg) and 3 g oa 3A molecular sieves was refluxed for 2 h. After filtration through celite the solvent was removed in vacuo to affordthe corresponding imine (Compound A1) as a glassy solid.

EXAMPLE III ##STR30##

To a solution of the crude imine A1 (240 mg) in 9 mL of methanol and 3 mL of water is added 30 mg of lithium hydroxide monohydrate and the mixture is stirred at room temperature for 2 h. After neutralization with dilute HCl and dilution with water, most of the methanol was removed in vacuo andthe resulting solid was collected to afford 2-(4-Methoxyphenyl)-benzimidazo 1,2-a!pyrazin-1-(5H)-one (Compound 1), m.p.>150° C.(dec).

EXAMPLE IV

The following compounds were prepared according to the procedure described in Examples I-IV:

a) 2-(2-Fluoro-5-methoxyphenyl)-benzimidazo 1,2-a!pyrazin-1(5H)- one (Compound 2), m.p.>150° C.(dec).

b) 2-Phenyl-benzimidazo 1,2-a!pyrazin-1(5H)-one (Compound 3). m.p.>150° C.(dec).

c) 2-(3-Methoxyphenyl)-benzimidazo 1,2-a!pyrazin-1(5H)-one (Compound 4). m.p.>150° C.(dec).

d) 2-(2-Fluorophenyl)-benzimidazo 1,2-a!pyrazin-1(5H)-one (Compound 5). m.p.>1 50° C.(dec).

e) 2-(3-Fluorophenyl)-benzimidazo 1,2-a!pyrazin-1(5H)-one (Compound 6). m.p.>150° C.(dec).

f) 2-(4-Ethoxyphenyl)-benzimidazo 1,2-a!pyrazin-1(5H )-one (Compound 7). m.p.>150° C.(dec).

g) 2-(3-Ethoxyphenyl)-benzimidazo 1,2-a!pyrazin-1(5H)-one (Compound 8). m.p.>150° C.(dec).

h) 2-(2-Fluoro-4-methoxyphenyl)-benzimidazo 1,2-a!pyrazin-1(5H)- one (Compound 9), m.p.>150° C.(dec).

i) 2-(2-Thienyl)-benzimidazo 1,2-a!pyrazin-1(5H)-one (Compound 10), m.p.>150° C.(dec).

j) 2-(4-Methoxyphenyl)-6,7,8,9-tetrahydro-benzimidazo 1,2- a!pyrazin-1(5H)-one (Compound 11), m.p.>150° C.(dec).

k) 2-(3-Methoxyphenyl)-6,7,8,9-tetrahydro-benzimidazo 1,2- a!pyrazin-1(5H)-one (Compound 12). m.p.>150° C.(dec,).

l) 2-(2-Fluoro-5methoxyphenyl)-6,7,8,9-tetrahydro-benzimidazo 1,2- a!pyrazin-1(5H)-one (Compound 13), m.p.>150° C.(dec).

m) 2-(4-Methoxyphenyl)-6,7,8,9-tetrahydro-benzimidazo 1,2- a!pyrazin-1(5H)-one (Compound 14). m.p.>150° C.(dec).

n) 2'-Phenyl-4,5,5', 6', 7', 9'-hexahydro-spiro furan-2,8'(3H)- benzimidazo 1,2-a!pyrazin-1'-one! (Compound 15).

o) 2'-(4-Methoxyphenyl)-5', 6', 7', 9'-tetrahydro-spiro (1,3)dioxolane- 2,8'-benzimidazo 1,2-a!pyrazin-1'-one! (Compound 16).

p) 2-(4-Methoxyphenyl)-pyrido 2,3-d!imidazo 1,2-a!pyrazin-1(5H)- one (Compound 17).

The invention and the manner and process of making and using it, are now described in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains, to make and use the same. It is to be understood that the foregoing describes preferred embodiments of the present invention and that modifications may be made therein without departing from the spirit or scope of the present invention as setforth in the claims. To particularly point out and distinctly claim the subject matter regarded as invention, the following claims conclude this specification. 

What is claimed is:
 1. A compound of the formula: ##STR31## or the pharmaceutically acceptable salts thereof wherein: R_(a) and R_(b) are independently hydrogen, halogen, lower alkoxy, or lower alkyl;A is nitrogen or CH; and B is nitrogen or CH, with the proviso that not both A and B are nitrogen simultaneously.
 2. A compound according to claim 1, wherein A is nitrogen.
 3. A compound according to claim 1, wherein B is nitrogen.
 4. A compound according to claim 1, wherein A and B are both CH. 